Hash-Kollision
Hash Collision
Hash-Kollision
A hash collision exists when two different inputs produce the same hash value. With a secure cryptographic hash function this should be practically impossible; if it nonetheless succeeds in a targeted way, the function is broken and unsuitable for security purposes. This is exactly what happened to MD5 and SHA-1.
History & facts. Collision resistance is a core property of cryptographic hash functions: it should be impossible to find two different inputs with the same hash. Research demonstrated practicable collision attacks first against MD5 and later against SHA-1, rendering both unusable for signatures and integrity proofs — an attacker could prepare a malicious document so that it carries the same hash as a harmless one. The SHA-2 (such as SHA-256) and SHA-3 families are still considered collision-resistant.
Outlook & recommendation. Practical consequence: broken functions such as MD5 and SHA-1 must no longer be used for security purposes — neither for signatures nor for integrity checking. In forensics, evidence integrity is therefore to be bound to current functions. If one encounters an old MD5 comparison, caution is advised: it serves at most for rough recognition, not as a robust proof of authenticity.